This invention relates generally to the production of protein or protein isolates and/or starch from cereal grains. In particular, this invention relates to a technique in which the bond between starch, on the one hand, and protein on the other is broken mechanically rather than by the conventional process of cooking. As a result, there is realized an increased recovery of a higher quality protein and intact granules of a higher quality pure starch.
It has been proposed heretofore to obtain a protein isolate from corn or other cereal grains. As is well known to nutritionists, agricultural commodities, such as cereal grains, may contain complete or nearly complete proteins and thus, if the protein were isolated, would be capable of providing a balanced diet for humans.
Heretofore, the extraction of isolated proteins from agricultural commodities has been made difficult by the chemical bonding which exists between protein and the starch constituents of the commodities. In prior, well known processes which involve some biochemical treatment or steps using one of these constituents, such as the yeast fermentation of corn or grains to produce ethanol, the starch/protein bond is broken by hydrolysis through cooking. However, breaking the bond by cooking, while making the starch and sugar content available for other uses, destroys the possibility of recovering the protein in a form useful as food.
James T. Lawhorn proposed, in U.S. Pat. No. 4,624,805, that, after an initial grinding step in which the grain is ground to "meal" size (250-600 microns), protein be isolated prior to the use of starches and sugars in an ethanol fermentation process. The protein is extracted with an alkali/alcohol solution either with or without sonification. Lawhorn teaches that the protein is recovered by ultrafiltration, with the dissolved sugars and starches in a permeate being concentrated by reverse osmosis for use in alcohol production.
It has been discovered by attempts to practice the Lawhorn process that the process as disclosed in the patent simply does not work on a commercial scale. First, by relying on chemicals and sonification to break the protein/starch bond, only minimal percentages of the available protein is extracted. Secondly, the ultrafiltration membranes described by Lawhorn foul and clog, and the desired continuous operation does not occur. However, the Lawhorn process does propose the separation of protein and other components of agricultural commodities by a process which avoids cooking and thereby would permit the recovery of a food graded protein isolate, if it worked on a commercial scale.
On a dry basis, the endosperm of corn makes up approximately 83% of the kernel and contains the bulk of the starch. Other cereal grains may vary somewhat in percentages of endosperm but are conceptually similar. The starch is present as granules of roughly 5-35 microns in size with the space therebetween filled with protein. This protein/starch matrix has to be broken to be able to recover either or both starch or protein. Intact starch granules are much more valuable than starch granules which are not intact. It should be noted that the structure of the granules themselves depends on the way in which amylose and amylopection are associated by intermolecular hydrogen bonds. Strong bonds give rise to crystalline areas and weak bonds to amorphous areas. Normal corn starch has a crystallinity in the range of 15-39%.
In the known processes for separating protein from starch, either the usefulness of protein and starch have been destroyed by the cooking and/or steeping process, or else the protein has been ineffectively recovered in the Lawhorn process. In my prior application Ser. No. 487,739, now abandoned, while a technique for mechanically breaking the starch/protein matrix, the starch granules are generally not left intact. Therefore, a process which effectively recovers quality protein and maintains starch granules intact has not been heretofore accomplished.